1. Field of the Invention
The present patent application for industrial invention relates to a low-noise fume extractor hood.
Although specific reference will be made hereinafter to an extractor hood for kitchen, the invention is also extended to an industrial extractor hood.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
As it is known, an extractor hood comprises a fan disposed in an extractor conduit provided with inlet filter. The fan is driven into rotation by an electric motor in order to extract fumes through the extraction conduit.
Said types of hoods are impaired by the very high noise level, both for the noise generated by motor, fan, and other mechanical moving parts, for the noise generated by the turbulent vertical air flow that is extracted in the conduit of the hood, and for the noise of the air passing through the inlet filter.
In order to solve such a drawback, at least partially, solutions provided with active noise suppression system are known.
Patent application EP 0 596 846 discloses a kitchen extractor hood provided with active noise suppression system. The hood is provided with microphones to detect noise, a loudspeaker generating a sound adapted to suppress noise and a control unit that controls the loudspeaker according to the noise detected by the microphones. The single loudspeaker is disposed with axis of emission substantially horizontal to the axis of conduit of hood, which is substantially vertical.
Patent applications US 2004/194776 and WO2010094718 disclose a hood with noise suppression system that provides for a loudspeaker disposed in central position inside the conduit of the hood. Said position of the loudspeaker results in a series of drawbacks, because of turbulence of the air flow extracted in the conduit of the hood that meets with the central support of the loudspeaker. Consequently, it is necessary to increase the power of motor, so that the flow of extracted air passes beyond the obstacle represented by the loudspeaker. Moreover, the loudspeaker in central position tends to get dirty because of direct contact with fumes extracted by the hood.
In any case, the known active noise suppression systems provide for one loudspeaker only, and do not allow for directivity of the sound signal beam, unless very expensive loudspeakers are used. Instead, according to the position of the hood, it is especially important to direct the sound beam of loudspeakers in a preferential direction with higher noise.
EP 0 671 720 discloses a hood with noise suppression system that can comprise one or more loudspeakers. However, EP 0 671720 illustrates only one loudspeaker with emission surface parallel to axis of conduit of hood.
WO01/6359 discloses a generic active noise reduction system not applied to an air extraction conduit. WO01/6359 teaches that loudspeakers must be generally disposed on a plane, but such a condition is not essential. WO01/6359 contains no teachings about how to dispose loudspeakers in case of air extraction conduit.
EP 0 961 087 discloses a fan provided with active noise suppression system.
Moreover, active noise suppression systems take into account only the noise generated by air extraction and do not consider the noise generated by vibration of walls of conduit housing fan and motor of hood.
The purpose of the present invention is to eliminate the drawbacks of the prior art by devising a low-noise fume extractor hood provided with active noise suppression system that does not obstruct the air extraction flow and at the same time allows for directivity of sound beam.
Another purpose of the present invention is to provide a low-noise extractor hood that is able to suppress also the vibration noise of the parts of the hood conduit.